Modern technologies of painting objects with liquid paints need air to be blown through the painting booth body by means of Air Supply Units, hereinafter referred to as ASU, to solve several technical tasks, namely:
A) to create a laminar air stream in the painting area with a velocity fast enough to evacuate the paint particle aerosol formed when spraying. The modern requirements for air stream velocity are 20-30 cm/sec, which is fast enough for high quality painting of, for example, car's body;
B) to evacuate vapors of Easy Flammable Liquids, hereinafter referred to as EFL, to a safe level (0.1-0.5 of Low Concentration Limit of Fire Propagation, or Low Explosive Limit, hereinafter referred to as LEL).
At present, one- or two-air fan ASUs are used [1, 2] comprising either an intake or an extract fan (a group of fans blocked), or both an intake and an extract fan (groups of fans) simultaneously which supply air into the painting zone (the painting booth body) in the “Paint” mode and/or extract it from the painting zone. Moreover, these devices simultaneously solve the above-mentioned tasks in the same air stream, i.e. an air stream sufficient to solve task A is fed from atmosphere through the painting zone during the painting process, task B being solved automatically because of a significantly higher air change than is necessary.
The above technological solutions are very simple because of a one-way air stream feed into the working area. Yet, this leads to an excessive consumption of fresh air and energy. Besides, many dispersed dry paint particles with a high content of toxic components combined with solvent vapors are emitted into atmosphere, and these emissions are strictly limited by ecological laws in most countries. Elimination of these contaminants from a significant air volume by means of filtration, sorption or burning requires bulky and expensive installations.
The technological task is therefore to improve the ASU operation in the “Paint” mode in order to decrease the energy costs for air which is supplied to and discharged from the painting zone, as well as it's treatment and subsequent ecological cleaning. The “Baking” mode is similar in all ASUs mentioned and is therefore not considered.
A car painting system and method are known, which comprise a number of consecutively installed painting booths, so that air is supplied from the first booth to the second, then third etc, until LEL is reached, with subsequent cleaning and/or extraction to atmosphere. The above painting system comprises several ASUs, fans, particle separator units, air valves etc. according to the number of painting booths in the system (see U.S. Pat. No. 3,807,291).
This method cannot be applied to a single object painting, a car or its parts after repair, in particular, and is intended for use in a number of automatic (or semiautomatic) painting booths in conveyor manufacturing lines.
There exists a method to feed air into a conveyor installation and a painting booth for this method which involves separation of the painting booth into a number of consecutive partitions when air into/from each partition is fed by separate fans through separate particle cleaners and the burning of EFL vapor follows the exit from the last partition (see U.S. Pat. No. 4,587,927).
Said method can only be used in conveyor automatic painting lines, and the conveyor painting booth is very complicated and not cost-effective, as it requires a great number of fans, particle cleaners, air valves etc. according to the number of partitions inside the painting booth.
The existing inventions require a significant volume of fresh air, which is equivalent to the standard way of paint booth air feeding (more than 20000 cubic meters per hour, as a rule). Solution of the task, i.e. more economical energy consumption in this group of innovations is based on the principle that when air is routed from one consecutive zone of the painting booth to the next, we use air that has already been heated in the previous zone, the energy consumption being thus lowered, but the air is still routed one-way and not returned to the previous zone, which means that the total amount of air volume has to be cleaned before being discharged to atmosphere after the last paint booth in the sequence, which still requires bulky and expensive systems of EFL vapor utilization.
Said methods and installations are used in conveyor painting lines, where the manufacturing volume is considerable and the technological process does not involve human labor. They are economically ineffective, however, for painting single objects on a small scale as well as for bodyshop repair, in absence of conveyor and when human presence in the painting booth is necessary. The bodyshop repair, for instance, involves painting of an immobilized car, and only one painting booth is usually available.
A painting booth for spray coating and a circulation system for the working area, and the method of air supply to paint booth (publication number WO 98/2808 of 2 Jul. 1998 under PCT application PCT/CH 97/00468 of 15 Dec. 1997), are much closer, in principle, to the method and installation proposed to realize the method.
Said method uses ASU to supply air from and discharge it back to atmosphere.
Said spray coating painting booth and circulation system for the working area include ASU to supply to and extract air from the booth. ASU comprises return air treatment and intake units connected together, as well as air ducts, an air regulation unit, hereinafter referred to as ARU, to extract air, ARU to feed air, recirculation and intake fans.
Said method and installation are not very reliable due to their complexity because the painting booth's working area, to realize the above method, has to be divided into multiple zones, namely: a paintwork zone, extraction zones and used air recirculation zone(s) combined with air stream regulation and/or stop air devices with their control units, fresh air feeding zone with separate stream regulation and/or stop air devices with their control units, up to 12 devices in all, let alone filters, light devices, a complicated installation to mechanically move objects being painted on the working area floor and ASU which is divided into sections to separately supply fresh and return air into the booth and extract it.
Exploitation of the above-mentioned painting booth and ASU is complicated because it is necessary to control/operate numerous air valves, which distracts the staff from the paint process and increases the time of fresh paint layer exposition to air stream before curing, which increases a possible deposition on the fresh painted surface. Different air supply zones in the booth's body and, consequently, different air flow volumes, also lead to a number of negative effects, in particular:
1) Low fire safety because of EFL accumulation in the main ASU volume and paint booth's body in the absence of fresh air feeding to those zones.
2) Formation of boundary turbulent air flows between fresh and recirculated air streams because of their different velocities, which leads to paint dispersed particles flying inside the booth and their subsequent potential deposition on the fresh painted surface.